The present invention relates generally to an electric motor assembly device, in particular for assembling a rotor with a commutator housing. The invention also provides a method for assembling the rotor into a stator using the electric motor assembly device.
In particular, the invention generally relates to an electric motor designed to drive automobile vehicle equipment, such as a window regulator, a sliding roof or a device for operating a seat, for example.
French patent 2,814,868 discloses such an electric motor including a stator and a commutator mounted on a rotor.
A commutator conventionally includes a commutator ring with a series of conducting segments on a periphery. The commutator ring is designed to be mounted integral with a rotor shaft. An electric motor generally includes a stator frame and the rotor shaft rotatively mounted in the stator. The electric motor also includes windings integral with the rotor shaft. Each winding is electrically connected to diametrically opposing commutator segments.
The commutator is generally mounted in a commutator housing integral with the stator after assembly. The commutator housing includes a carrier with a central opening designed to receive the commutator and to allow the rotor shaft to pass through the carrier of the commutator housing. The carrier is made of an insulating material, such as, for example, plastics material.
The commutator housing also includes at least two brushes that are diametrically opposed with respect to the commutator. The brushes are designed to make contact with the commutator segments during rotation of the commutator segments integral with the rotor shaft. The brushes are electrically connected to a source of electrical power.
When the electric motor is being assembled, and in particular when the commutator is being assembled into the commutator housing, the brushes must be kept spaced from their point of contact with the commutator segments. After this, when assembly is completed, the brushes need to be brought into contact with the commutator segments. The mechanical contact between the brushes and commutator segments needs to be guaranteed to insure a good electrical contact with the windings via the commutator segments.
Thus, the brushes need to be held in a first position (an assembly position) when the commutator is being assembly. Then, the brushes need to be held in a second position guaranteeing contact (a contact position) to ensure electricity is supplied to the commutator segments.
Additionally, while the electric motor is being assembled, the rotor shaft is not always suitably guided when inserted through the commutator housing. The rotor shaft can strike against contact surfaces of the brushes, even when the brushes are in the assembly position (the position where the brushes are spaced from a passage for the rotor shaft).
A known commutator housing is, for example, installed on motors sold by the assignee and identified by reference 420143, which includes a brush locking device. The commutator housing of the prior art is shown diagrammatically in FIGS. 1a and 1b, which respectively show the brushes in the assembly position and in the contact position.
The commutator housing includes a plastic housing carrier 1 on which two cages 8 are provided. Each cage 8 receives a brush 5, and each brush 5 includes an electrical connection constituted by a copper pigtail 6 (only one connection is illustrated). The commutator housing shown does not include the commutator, but has a central opening 2 designed to receive a commutator ring and a rotor shaft passing therethrough.
As shown in FIG. 1a, the brushes 5 are retracted to an assembly position (or a retracted position) behind the cages 8 at a side opposite the central opening 2 designed to receive the commutator. A spring 9 keeps each brush 5 in the assembly position when the rotor shaft is mounted through the central opening 2. The cages 8 protect the brushes 5 against possible impact with a badly guided rotor.
In the contact position, shown in FIG. 1b, the brushes 5 are housed inside the cages 8. The spring 9 exerts pressure on a back face of the brushes 5 to urge the brushes 5 towards the commutator.
Thus, the spring 9 has the dual function of keeping the brush 5 in the assembly position, and then in the contact position. The spring 9 nevertheless constitutes a key part that is separate from the housing carrier 1. The housing carrier 1 needs to be manufactured separately and then assembled onto the commutator housing. Further, the point where the spring 9 bears on the brush 5 needs to be located on top of or behind the brush 5 to ensure the brush 5 is put into the assembly position and then the contact position, requiring a specific operation which is frequently manual and costly. Further, electrical connection of the brush 5 is also insured by the copper pigtail 6, which is an additional part.
Multiplying the number of parts needed for correct operation of the commutator housing increases costs and complicates its manufacture. Further, shifting the brushes 5 from the assembly position increases its cost and requires a specific assembly operation.
Further, U.S. Pat. No. 4,596,941 discloses a commutator housing including a carrier with a central opening, a commutator and brushes secured onto flexible brush holders. In the assembly position, the brush holders are restrained by holding pins integral with the carrier. Local deformation of the carrier pushes a release pin to release the brush holders from the assembly position. The release pin raises the brush holder, then clears a restraining abutment and returns (under spring recall) into an operating position against the commutator.
The commutator housing does not adequately protect the brushes in the assembly position. In effect, even when the brushes are spread apart, the rotor shaft can strike the contact surface of the brushes while the rotor shaft is being introduced through the opening in the commutator housing. Further, shifting the brushes from the assembly position to a contact position always requires the manual intervention of an operator to push in the release pin.
There is consequently a need for an assembly device which protects brush surfaces in an assembly position, and which allows brushes to move from the assembly position to a contact position in a simple, efficacious and automatic manner.